Import and export from/to contest.yaml
Move import/export to separate subpage
Add initial support for tsv file export.
Add scoreboard.tsv export.

Filter out any tab character that may be in the fields.
Basic support for importing groups and teams tsv formats.

These formats are specified in the ICPC validator standard and have
been tested as such. It hasn't yet been tested with real data
coming out of the ICPC registration system.
Need to add audit log to import.
Fix contest YAML import to new timestamps, ignore languages, and a few minor fixes.
Fix check while importing tsv files.
Chop off second precision of freeze and endtime in contest.yaml.

Our contest relative times do not support second precision and we
don't see it as a useful thing to implement, so just chop it off
on import to prevent data validation problems later.
On import replace non-IDENTIFIER_CHARS with a _.

Otherwise the interface breaks if we import affiliations with e.g.
a space. This fixes the problem for now; maybe a better approach
is to get rid of this primary key in team_affiliation.
Affiliation long and short name fields were switched.
update link to dedicated import/exportpage
Skip clarification answers/categories for now.

DOMjudge master doesn't support that technology and it's not quite essential.
Can easily be added / ported later.
Add externalid field to team table to reference foreign registration systems.

This field has no semantics inside DOMjudge but exists only to establish
a relation to any external team registration system, for example the ICPC
system.
Fixes for changes in DOMjudge master.